1. FIELD OF THE INVENTION
The field of the invention is drill rod apparatus used in mineral exploratory type borehole drilling employing double wall drill tubes to recover grindings and cuttings for analysis from the bottom of the borehole.
2. DESCRIPTION OF THE RELATED ART
In the field of the invention it is necessary to drill exploratory boreholes in areas of expected mineralization to obtain data relating to the presence and concentration of an ore body or potential ore body. To this end, information must be known concerning the ore products encountered by the drill bit relative to its depth below the ground surface. Several types of methods are available for obtaining such data. For example, core samples of the earth may be obtained through the means of rotary diamond drilling wherein an annular elongated cylinder is drilled leaving a resultant solid cylindrical core which is then brought to the surface for analysis by raising the drill rod and bit. Such method is, in addition to being slow and tedious, very expensive. Other methods of exploratory earth boring are available, such as drilling a borehole utilizing a rotary bit and concurrently bringing to the surface the cuttings or grindings resulting from the drilling process as the process is continuing. Such a method provides continuous analysis as the drilling progresses.
In addition, a borehole may be sunk by percussion drilling wherein fragments of the portion of the earth being hammered by the drill rod bit are loosened and simultaneously brought to the surface for analysis.
The drill rod for accomplishing methods of earth boring wherein rock fragments or drill cuttings and grindings are brought to the surface for analysis without the need for raising the drill rod is the aim of the subject inventive reverse circulation drill rod.
More particularly, it is known to use dual wall or double wall tubular concentric drill rod as the means for transmitting torque to the rotary bit, or air to a percussion core bit, while at the same time bringing up the rock fragments and drill cuttings. This is accomplished for both cases by injecting a fluid in the cylindrical space annulus between the two concentric tubes (the outer tube and the inner tube) at the ground surface, the fluid then pumped, under pressure, to the area of the rotary bit or percussion core bit at the lower end of the drill rod. Then the rock fragments or cuttings are removed to the ground surface by the injected fluid as the rock fragments and bit grindings are generated. These fragments or grindings are transmitted through the conduit provided by the inner tube, sometimes referred to as an exit tube. Either a liquid or gas may be used as the fluid.
Connecting sections or stands of the outer tube are pins and boxes, each outer tube section having a threaded pin at one end and a threaded box at the other, the tube sections adapted to be joined together to form long lengths of drill rod by connecting pins with boxes. Typically, a section may be 10 to 25 feet in length.
Problems which have been encountered in reverse circulation drill rods are restrictions to the flow of fluid downward in the outer cylindrical space annulus between the outer and inner tubes caused in many cases by the fluid attempting to get through the pins and boxes at each end of the outer tube and by the various schemes by which the inner tube is attached to the pin and box in each stand of drill rod. In addition, each pin and each box must align the inner tube so that it operably connects to the inner tube in the next section of the drill rod with minimal opportunity for loss of the fluid containing the rock fragments or bit cuttings moving interiorly upward through the inner tube, or the escape of fluid into the inner tube from the cylindrical space annulus at the inner tube joints as the fluid is being pumped downward in the drill rod.
In the past, it has been common to utilize schemes wherein the inner tube sections residing in each outer tube stand or section is butt joined with a resilient seal. However, disadvantages of using a separate seal at the inner tube joint are that in many cases these seals will be damaged in the process of inserting them between the sections of inner tube, and because each seal must be separately placed between the sections of inner tube, the process becomes very time consuming and adds considerably to the cost of drilling.
In addition, for those types of reverse circulation drill rod which have inner tubes joined by threading sections of inner tube together, in many cases, to assure a fit between inner tubes, the threads on the inner tube must be indexed with the threads on the pin and box. -n addition, it is readily apparent that if the outer tube and the inner tube are fixed lengths, placement of the pin and the box upon the outer tube must be precise in order that the length of the outer tube plus its pin and box must be precision related to the length of the inner tube. Otherwise, the threads, although indexed as to where each rotationally starts, may not be engaged simultaneously, and insufficient sealing between inner tubes will result if there are variances between each length of the outer tube plus its pins and boxes and the inner tube. Such variances will result in inadequate sealing of the joints of the inner tube.
Thus it is apparent that it would be useful to provide a reverse circulation drill rod section which provides for longitudinal freedom of the inner tube relative to the outer tube and its box and pin where, in connecting multiple lengths, of the drill rod, errors in inner tube length or outer tube and its box and pin lengths tend to compensate for each other while not requiring resilient seals between each section of inner tube.
Accordingly, there would be an advantage of providing such a reverse circulation drill rod sections which permits movement of the inner tube relative to the outer tube for purposes of attaching one drill rod section to another, while also providing minimum resistance to travel of fluid down through the cylindrical space annulus of the drill rod sections. In addition, having such drill rod sections so constructed as to require minimum effort and time on the part of the operators in connecting one section to another would also be obviously advantageous.